Digital camera

ABSTRACT

In a digital camera including an electronic flash device using a light-emitting diode as a flash light source, white balance correction is performed by using a white balance correction value corresponding to a color temperature of light actually emitted from the electronic flash device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital camera and particularlyrelates to a digital camera comprising an electronic flash device usinga light-emitting diode (LED) as a flash light source.

2. Description of the Related Art

In general, a xenon tube is used as a light source in an electronicflash device of a camera. However, an electronic flash device using axenon tube as a light source can emit only instant light of severalmilliseconds, so that flash shooting cannot be performed while a shutteris released slowly. Further, since a xenon tube has a spectralcharacteristic close to a daylight color, flash shooting for backlightcorrection in the morning and evening results in a picture with anunnatural color. Hence, in order to solve the defect of such anelectronic flash device using a xenon tube as a light source, anelectronic flash device using an LED as a light source is proposed(e.g., Japanese Patent Application Publication No. 2002-116481).

However, since an LED emits light varied in color temperature amongproducts, when an LED is used as a flash light source of a digitalcamera, a white balance correction result is varied among products.

Moreover, an LED emits light varied in color temperature according to anambient temperature and an applied current, and a white balancecorrection result is varied according to an ambient temperature and anapplied current.

The present invention is devised in view of such circumstances and hasas its objective the provision of a digital camera achieving an image ofa stable color shade during flash shooting using an LED as a flash lightsource.

SUMMARY OF THE INVENTION

In order to attain the above objective, first aspect of a presentinvention provides a digital camera having an electronic flash deviceusing a light-emitting diode as a flash light source, comprising: astorage device which stores correction information for correcting whitebalance of an image obtained by flash shooting using the electronicflash device, the storage device storing the correction information setbased on a detection result of a color temperature of light actuallyemitted from the electronic flash device; and a white balance correctingdevice which corrects white balance of the image obtained by flashshooting using the electronic flash device based on the correctioninformation stored in the storage device.

According to the first aspect, the white balance correction informationis set based on a detection result of a color temperature of lightactually emitted from the electronic flash device, and the white balanceof the image obtained by flash shooting is corrected based on the setcorrection information. Hence, even when light emitted from theelectronic flash device is varied in color temperature among products,it is possible to obtain images of the same color shade.

Further, in order to attain the above object, second aspect of a presentinvention provides a digital camera having an electronic flash deviceusing a light-emitting diode as a flash light source, comprising: astorage device which stores correction information for correcting whitebalance of an image obtained by flash shooting, a white balancecorrecting device which corrects white balance of the image obtained byflash shooting based on the correction information stored in the storagedevice, a modification information storage device which storesmodification information for correcting the correction informationstored in the storage device, the modification information storagedevice storing the modification information required to make thecorrection information stored in the storage device coincident withcorrection information set based on a detection result of a colortemperature of light actually emitted from the electronic flash device,a modifying device which modifies the correction information based onthe modification information stored in the modification informationstorage device; and the white balance correcting device corrects thewhite balance of the image obtained by flash shooting based on thecorrection information modified by the modifying device.

According to the second aspect of the present invention, the whitebalance correction information stored in the storage device is modifiedso as to coincide with the white balance correction information setbased on a detection result of a color temperature of light actuallyemitted from the electronic flash device, and the white balance of theimage obtained by flash shooting is corrected based on the modifiedcorrection information. Hence, even when light emitted from theelectronic flash device is varied in color temperature among products,it is possible to obtain images of the same color shade.

Moreover, in order to attain the above object, third aspect of a presentinvention provides a digital camera having an electronic flash deviceusing a light-emitting diode as a flash light source, comprising: astorage device which stores correction information for correcting whitebalance of an image obtained by flash shooting, a white balancecorrecting device which corrects white balance of the image obtained byflash shooting based on the correction information stored in the storagedevice, a temperature detecting device which detects an ambienttemperature of the light-emitting diode, a modification informationstorage device which stores modification information for modifying thecorrection information stored in the storage device, the modificationinformation storage device storing the modification information of thecorrection information based on a change in an ambient temperature ofthe light-emitting diode, a modifying device which modifies thecorrection information stored in the storage device based on a detectionresult of the temperature detecting device and the modificationinformation stored in the modification information storage device; andthe white balance correcting device corrects white balance of the imageobtained by flash shooting based on the correction information modifiedby the modifying device.

According to the third aspect of the present invention, the whitebalance correction information stored in the storage device is modifiedaccording to a change in the ambient temperature of the light-emittingdiode, and the white balance of the image obtained by flash shooting iscorrected based on the modified correction information. Hence, even whenthe light-emitting diode changes in ambient temperature and lightemitted from the electronic flash device changes in color temperature,it is always possible to obtain images of the same color shade.

In order to attain the above objective, fourth aspect of a presentinvention provides a digital camera having an electronic flash deviceusing a light-emitting diode as a flash light source, comprising: astorage device which stores correction information for correcting whitebalance of an image obtained by flash shooting, a white balancecorrecting device which corrects white balance of an image obtained byflash shooting based on the correction information stored in the storagedevice, a current detecting device which detects a value of currentapplied to the light-emitting diode, a modification information storagedevice which stores modification information for the correctioninformation based on a change in a value of current applied to thelight-emitting diode, the modification information storage devicestoring the modification information for modifying the correctioninformation stored in the storage device, a modifying device whichmodifies the correction information stored in the storage device basedon a detection result of the current detecting device and themodification information stored in the modification information storagedevice; and the white balance correcting device corrects the whitebalance of the image obtained by flash shooting, based on the correctioninformation modified by the modifying device.

According to the fourth aspect of the present invention, the whitebalance correction information stored in the storage device is modifiedaccording to a change in current applied to the light-emitting diode,and the white balance of the image obtained by flash shooting iscorrected based on the modified correction information. Hence, even whencurrent applied to the light-emitting diode changes and light emittedfrom the electronic flash device changes in color temperature, it isalways possible to obtain images of the same color shade.

As described above, according to the present invention, white balancecorrection is performed based on a color temperature of light actuallyemitted from an electronic flash device. Thus, even when an LED is usedas a flash light source, it is always possible to obtain an image of astable color shade.

Further, since white balance correction is performed according to achange in ambient temperature or a change in current applied to the LED,it is always possible to obtain an image of a stable color shade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view showing one embodiment of a digitalcamera according to the present invention;

FIG. 2 is a sectional view showing the configuration of a light-emittingpart of an electronic flash device;

FIG. 3 is a block diagram showing the internal configuration of thedigital camera;

FIG. 4 is a block diagram showing the internal configuration of adigital camera according to Embodiment 3;

FIG. 5 is an xy chromaticity diagram showing a change in colortemperature relative to a change in ambient temperature T of an LED;

FIG. 6 is a block diagram showing the internal configuration of adigital camera according to Embodiment 4; and

FIG. 7 is an xy chromaticity diagram showing a change in colortemperature relative to a change in current I applied to an LED.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of a digital camera according to the presentinvention will be described below in accordance with the accompanyingdrawings.

FIG. 1 is a front perspective view showing an embodiment of a digitalcamera 10 according to the present invention. As shown in FIG. 1, thefront of a camera body 12 comprises a taking lens 14, a finder window16, an electronic flash device 18, a flash light control window 20, andso on. The top surface comprises a release button 22, a power supplyswitch 24, and so on. Further, the back (not shown) of the camera body12 comprises a finder eyepiece, a liquid crystal monitor, variousoperation buttons (e.g., a zoom key, a mode button, a menu button, across button) and so on.

FIG. 2 is a sectional view showing the configuration of a light-emittingpart of the electronic flash device 18 which is mounted in the digitalcamera 10 shown in FIG. 1. As shown in FIG. 2, the light-emitting partof the electronic flash device 18 is constituted of a light-emittingdiode (LED) 26 serving as a light source, a reflector 28 for reflectingforward light emitted from the LED 26, and a diffuser panel 30 fordiffusing light emitted from the LED 26.

The LED 26 is mounted on a circuit board 32 and emits white light withhigh intensity. The reflector 28 is attached to the circuit board 32 soas to surround the LED 26. Further, the diffuser panel 30 is integrallyattached into the reflector 28 and diffuses light emitted with highdirectivity from the LED 26.

FIG. 3 is a block diagram showing the internal configuration of thedigital camera 10. As shown in FIG. 3, behind a lens unit 34 includingthe taking lens 14 and an iris 15, a solid-state image sensing device(CCD) 36 is disposed. On a light-receiving surface of the CCD 36, anumber of photosensors are arranged two-dimensionally. A subject imageformed on the light-receiving surface of the CCD 36 via the taking lens14 and the iris 15 is converted to signal charge corresponding to anincident light quantity by the photosensors. Then, the signal chargeaccumulated in the photosensors is read into a shift register by a readgate pulse applied from a CCD driving circuit 38, and the signal chargeis sequentially read by a register transfer pulse as a voltage signalcorresponding to the signal charge.

Besides, the CCD 36 can sweep the accumulated signal charge by using ashutter gate pulse, so that time for accumulating charge (shutter speed)can be controlled (so-called electronic shutter function).

Voltage signals sequentially read from the CCD 36 are applied to acorrelated double sampling circuit (CDS circuit) 40. R, G, and B signalsof each pixel are subjected to sampling hold therein and are applied toan AD converter 42. The AD converter 42 converts analog R, G, and Bsignals, which are sequentially applied from the CDS circuit 40, todigital R, G, and B signals and outputs the signals therefrom.

Moreover, the CCD driving circuit 38, the CDS circuit 40, and the ADconverter 42 are driven in synchronization with one another by a timingsignal applied from a timing generation circuit (TG) 44.

The digital R, G, and B signals outputted from the AD converter 42 aretemporarily stored in a memory 46 and are applied to a digital signalprocessing circuit 48.

The digital signal processing circuit 48 is constituted of asynchronization circuit 50, a white balance correction circuit 52, agamma-correction circuit 54, a YC signal generation circuit 56, a memory58, and so on.

The synchronization circuit 50 sequentially synchronizes the R, G, and Bsignals of each pixel which are read from the memory 46, and outputs theR, G, and B signals simultaneously to the white balance correctioncircuit 52.

The white balance correction circuit 52 comprises multipliers 52R, 52G,and 52B for increasing or reducing the digital values of the R, G, and Bsignals, respectively. The R, G, and B signals inputted from thesynchronization circuit 50 are applied to the multipliers 52R, 52G, and52B, respectively. Further, a white balance correction value (gainvalue) W (W_(R), W_(G), W_(B)) for white balance control is applied froma central processing unit (CPU) 60 to the other inputs of themultipliers 52R, 52G, and 52B. The multipliers 52R, 52G, and 52B eachperform a multiplication on two inputs and output R′, G′, and B′signals, which have been subjected to white balance correction bymultiplication, to the gamma-correction circuit 54.

The detail will be discussed later regarding the white balancecorrection value W applied from the CPU 60 to the white balancecorrection circuit 52.

The gamma-correction circuit 54 changes input/output characteristics sothat the R′, G′, and B′ signals having been subjected to white balancecorrection have desired gamma characteristics, and the gamma-correctioncircuit 54 outputs the signals to the YC signal generation circuit 56.

The YC signal generation circuit 56 generates a luminance signal Y andchroma signals Cr and Cb from the R, G, and B signals having beensubjected to gamma correction. The luminance signal Y and chroma signalsCr and Cb (YC signals) are stored in the memory 58 having the samememory space as the memory 46.

Here, the YC signal in the memory 58 is read and outputted to a liquidcrystal monitor 62, so that a through image, a taken static image, andso on can be displayed on the liquid crystal monitor 62 which isprovided on the back of the camera body 12.

Further, the YC signal after shooting is compressed in a predeterminedformat by a compression/expansion circuit 64 and is recorded in arecording medium such as a memory card by a recording section 66.

Further, in a reproduction mode, image data recorded in a memory cardand so on is expanded by the compression/expansion circuit 64 and isoutputted to the liquid crystal monitor 62, so that a reproduced imageis displayed on the liquid crystal monitor 62.

The CPU 60 exercises control over circuits based on an input from acamera operation section 68 including the release button 22, the powersupply switch 24, and so on, and the CPU 60 performs autofocus control,automatic exposure control, white balance control, and so on.

For example, autofocus control is performed by a contrast AF system inwhich the movement of the taking lens 14 is controlled so that a Gsignal in a specific focus area has the maximum high-frequencycomponent. The CPU 60 controls the movement of the taking lens 14 via alens driving section 14A so that a G signal in a specific focus area hasthe maximum high-frequency component.

Automatic exposure control is performed by calculating a luminance of asubject (shooting EV value) based on an integrated value of the R, G,and B signals and controlling an aperture and a shutter speed based onthe calculated shooting EV value. The CPU 60 determines an aperturevalue and a shutter speed based on the shooting EV value, controls theiris 15 via an iris driving section 15A so as to have the determinedaperture value, and controls a charge accumulation time via the CCDdriving circuit 38 so as to have the determined shutter speed.

Moreover, the CPU 60 decides whether or not flash shooting is necessarybased on the shooting EV value. When flash shooting is necessary, flashlight is emitted from the electronic flash device 18 via a flashlight-emitting circuit 18A.

White balance control is performed by determining a light source type(color temperature of a field), determining a white balance correctionvalue W (W_(R), W_(G), W_(B)) suitable for the determined light sourcetype, and outputting the determined white balance correction value W tothe multipliers 52R, 52G, and 52B of the white balance correctioncircuit 52 (upon normal shooting).

A light source type (color temperature of a field) is determined asfollows: first whole screen is divided into a plurality of areas (e.g.,8*8) based on the R, G, and B signals temporarily stored in the memory46, and an average integrated value for each color of the R, G, and Bsignals is calculated in each of the divided areas. The averageintegrated value of the R, G, and B signals for each of the dividedareas is calculated by an integration circuit 70 and is applied to theCPU 60. Multipliers 72R, 72G, and 72B are provided between theintegration circuit 70 and the CPU 60, and an adjusted gain value foradjusting a variation between devices is applied to the multipliers 72R,72G, and 72B. The CPU 60 discriminates a light source type such as daylight (fine whether), shade-cloudy, a fluorescent light, and a tungstenlamp based on the average integrated value of the R, G, and B signalsfor each of the divided areas. The average integrated value has beenapplied from the integration circuit 70 via the multipliers 72R, 72G,and 72B.

In the discrimination of the light source type, ratios R/G and B/G arecalculated for each of the divided areas regarding an average integratedvalue for each color of the R, G, and B signals. Subsequently, thedetection frames, each of them indicates a range of color distributioncorresponding to a specific light source type, are set on a graph wherea horizontal axis represents R/G and a vertical axis represents B/G.Then, the number of areas existing in each detection frame is calculatedbased on the ratios R/G and B/G for each obtained area, and the lightsource type is discriminated based on the luminance level of a subjectand the number of the areas existing in each detection frame (JapanesePatent Application Publication No. 2000-224608).

Besides, the method of automatically determining a light source type(color temperature of a field) based on the R, G, and B signals obtainedfrom the CCD 36 is not limited to the present embodiment.

When the light source type (color temperature of a field) is determinedthus, the CPU 60 determines a white balance correction value W (W_(R),W_(G), W_(B)) suitable for the light source type and outputs thedetermined white balance correction value W to the multipliers 52R, 52G,and 52B of the white balance correction circuit 52. Thus, the R′, G′,and B′ signals having been subjected to white balance correction areoutputted to the gamma-correction circuit 54 from the multipliers 52R,52G, and 52B.

The white balance correction value W (W_(R), W_(G), W_(B)) is determinedby making reference to a table recorded in a ROM 74. The table recordsthe white balance correction value W corresponding to each light sourcetype (color temperature of a field). When a light source type (colortemperature of a field) is determined, the white balance correctionvalue W corresponding to the light source type is uniquely determined.The ROM 74 records an operation program of a camera and various kinds ofdata in addition to the table indicating a relationship between thelight source type and the white balance correction value.

As described above, in normal shooting not using the electronic flashdevice 18, a light source type is determined upon shooting, a whitebalance correction value W (W_(R), W_(G), W_(B)) suitable for thedetermined light source type is determined based on a table, and thedetermined white balance correction value W is outputted to themultipliers 52R, 52G, and 52B of the white balance correction circuit 52to perform white balance correction.

On the other hand, in the case of flash shooting using the electronicflash device 18, a light source type is not determined but a whitebalance correction value W_(O) (W_(OR), W_(OG), W_(OB)) corresponding toa color temperature of flash light is used to perform white balancecorrection. That is, in the case of flash shooting, the CPU 60 reads thewhite balance correction value (white balance correction value suitablefor a color temperature of flash light) W_(O) (W_(OR), W_(OG), W_(OB))for flash shooting from the ROM 74 and the CPU 60 outputs the whitebalance correction value W_(O) to the multipliers 52R, 52G, and 52B ofthe white balance correction circuit 52.

In this case, the ROM 74 records, as a white balance correction valuefor flash shooting, a white balance correction value W_(O) (W_(OR),W_(OG), W_(OB)) for emitting flash light of a reference colortemperature T_(O). Therefore, by emitting flash light having the samecolor temperature from the electronic flash device 18 as the referencecolor temperature T_(O) and performing shooting, an image is obtainedwith fine color balance.

However, the LED serving as a light source of the electronic flashdevice 18 emits light varied in color temperature among elements andthus the LED does not always emit light having the same colortemperature as the reference color temperature.

Thus, in the digital camera of the present embodiment, a colortemperature T₁ of light actually emitted from the electronic flashdevice 18 is measured and a white balance correction value W₁ (W_(1R),W_(1G), W_(1B)) suitable for the color temperature T₁ is used to performwhite balance correction upon flash shooting. To be specific, whitebalance correction upon flash shooting is performed as below.

First, a color temperature T₁ of light actually emitted from theelectronic flash device 18 is measured. Then, a white balance correctionvalue W₁ (W_(1R), W_(1G), W_(1B)) suitable for the color temperature T₁is calculated. A difference ΔW (ΔW=W_(O)−W₁) between the determinedactual white balance correction value W₁ (W_(1R), W_(1G), W_(1B)) andthe reference white balance correction value W_(O) (W_(OR), W_(OG),W_(OB)) recorded in the ROM 74 is calculated, and the difference ΔW isrecorded as a modification value in an EEPROM 76. That is, amodification value ΔW (ΔW_(R), ΔW_(G), ΔW_(B)) is calculated forcorrecting the reference white balance correction value W_(O), which isrecorded in the ROM 74, to the white balance correction value W₁(W_(1R), W_(1G), W_(1B)) suitable for the color temperature T₁ of flashlight actually emitted from the electronic flash device 18, and thecorrection value ΔW is recorded in the EEPROM 76 (ΔW_(R)=W_(OR)−W_(1R),ΔW_(G)=W_(OG)−W_(1G), ΔW_(B)=W_(OB)−W_(1B)).

The CPU 60 reads the reference white balance correction value W_(O)(W_(OR), W_(OG), W_(OB)) for flash shooting from the ROM 74 and readsthe modification value ΔW (ΔW_(R), ΔW_(G), ΔW_(B)) from the EEPROM 76upon flash shooting. Then, the reference white balance correction valueW_(O) (W_(OR), W_(OG), W_(OB)) is corrected to the white balancecorrection value W₁ (W_(1R), W_(1G), W_(1B)) suitable for the colortemperature T₁ of actual flash light by using the modification value ΔW(ΔW_(R), ΔW_(G), ΔW_(B)), and the corrected value is outputted to themultipliers 52R, 52G, and 52B of the white balance correction circuit52.

Hence, even when the LED emitting light varied in color temperature isused as a flash light source, each product of camera can obtain an imageof the same color shade without being varied in color balance.

Besides, a color temperature T₁ of actual flash light is measured by acolor temperature measuring device after the digital camera 10 ismanufactured. That is, flash light is actually emitted from theelectronic flash device 18 and the color temperature of the light ismeasured by the color temperature measuring device. Then, a whitebalance correction value W₁ suitable for the measured color temperatureT₁ of the light is calculated, a difference ΔW is calculated from thereference white balance correction value W_(O) for flash shooting thatis recorded in the ROM 74, and a modification value is obtained.

The obtained modification value ΔW is written in the EEPROM 76 by usinga communicating function (e.g., USB, IEEE 1394, etc.) provided in thedigital camera 10. That is, for example, the digital camera 10 and apersonal computer are connected to each other via a USB cable, the dataof the modification value is transmitted from the personal computer tothe digital camera, and the transmitted data of the modification valueis written in the EEPROM 76.

Further, the data of the modification value may be obtained by using arecording medium for recording images. That is, the following processmay be applicable: the recording medium having recorded the data of themodification value is loaded into the digital camera 10, the data of themodification value is acquired from the recording medium, and the datais written in the EEPROM 76.

Moreover, the recording device for recording the data of themodification value is not limited to the EEPROM and thus anotherrecording device may be used.

The following will describe Embodiment 2 of a digital camera accordingto the present invention. The basic configuration of the device is thesame as the digital camera of Embodiment 1 and thus the explanationthereof is omitted.

In the digital camera of Embodiment 1, the white balance correctionvalue W₁ suitable for the color temperature of actual flash light isobtained by correcting the white balance correction value W_(O), whichis recorded in the ROM 74, by using the modification value ΔW recordedin the EEPROM 76.

In a digital camera 10 of the present embodiment, a white balancecorrection value W₁ suitable for the color temperature of actual flashlight is recorded in an EEPROM 76, and the white balance correctionvalue W₁ recorded in the EEPROM 76 is used to perform white balancecorrection.

In a method of recording the white balance correction value W₁ in theEEPROM 76, recording is performed by using a communicating function anda recording medium that are provided in the digital camera, just likethe digital camera 10 of Embodiment 1.

In the digital camera of the present embodiment, a CPU 60 reads a whitebalance correction value W₁ (W_(1R), W_(1G), W_(1B)) from the EEPROM 76and outputs the value to multipliers 52R, 52G, and 52B of a whitebalance correction circuit 52 to perform white balance correction.

Thus, even when an LED emitting light varied in color temperature isused as a flash light source just like the digital camera of Embodiment1, each product of camera can obtain an image of the same color shadewithout being varied in color balance.

Additionally, the table of a white balance correction value of normalshooting may be recorded in the EEPROM 76 along with a white balancecorrection value of flash shooting.

FIG. 4 is a block diagram showing the internal configuration ofEmbodiment 3 according to a digital camera of the present invention.

As shown in FIG. 4, a digital camera 100 of the present embodiment isdifferent from the digital camera 10 of Embodiment 1 in that anelectronic flash device 18 comprises a temperature sensor 102 fordetecting an ambient temperature of an LED serving as a flash lightsource. Since the other configurations are the same as the digitalcamera 10 of Embodiment 1, the same components as the digital camera 10of Embodiment 1 are indicated by the same reference numerals and thusexplanation thereof is omitted.

The LED serving as a flash light source emits light varied in colortemperature according to a change in ambient temperature. FIG. 5 is anxy chromaticity diagram showing a change in color temperature relativeto a change in an ambient temperature T of the LED (current (forwardcurrent) applied to the LED is 20 mA). As shown in FIG. 5, when theambient temperature of the LED changes from a high temperature to a lowtemperature, the color temperature of light emitted by the LED changesaccordingly from a high temperature to a low temperature.

Therefore, when white balance correction is performed by using aconstant white balance correction value on image data obtained by flashshooting, an ambient temperature change of the LED may result in imagesof different color shades.

Hence, in the digital camera 100 of the present embodiment, a whitebalance correction value is corrected according to a change in theambient temperature of the LED.

As shown in FIG. 4, an electronic flash device 18 comprises atemperature sensor 102 for detecting the ambient temperature of the LEDserving as a light source. The ambient temperature of the LED that isdetected by the temperature sensor 102 is inputted to the CPU 60 via anAD converter 104.

On the other hand, an EEPROM 76 records a table indicating acorrespondence relationship between an ambient temperature T of the LEDand a white balance correction value W_(T) (W_(TR), W_(TG), W_(TB)). Bymaking reference to the table, the white balance correction value W_(T)(W_(TR), W_(TG), W_(TB)) is uniquely determined according to the ambienttemperature T of the LED.

Upon flash shooting, the CPU 60 acquires the ambient temperature T ofthe LED via the AD converter 104 from the temperature sensor 102 anddetermines the white balance correction value W_(T) (W_(TR), W_(TG),W_(TB)), which corresponds to the ambient temperature T, based on thetable recorded in the EEPROM 76. Then, the CPU 60 outputs the determinedwhite balance correction value W_(T) (W_(TR), W_(TG), W_(TB)) tomultipliers 52R, 52G, and 52B of a white balance correction circuit 52and performs white balance correction on taken image data.

Thus, even when the LED changes in ambient temperature and light emittedfrom the LED changes in color temperature, it is always possible toobtain an image with stable color balance.

In the present embodiment, the white balance correction value W_(T)(W_(TR), W_(TG), W_(TB)) at each ambient temperature T of the LED isrecorded as a table in the EEPROM 76. A ROM 74 may record a referencewhite balance correction value, for example, a white balance correctionvalue W₂₀ (W_(20R), W_(20G), W_(20B)) when the LED has an ambienttemperature T of 20° C., and the EEPROM 76 may record a modificationvalue ΔW_(T) (modification value of the reference white balancecorrection value W₂₀ at each ambient temperature T) as a table at eachambient temperature T of the LED.

In this case, the CPU 60 acquires the modification value ΔW_(T)corresponding to the ambient temperature T from the table recorded inthe EEPROM 76 and corrects the reference white balance correction valueW₂₀. Then, the CPU 60 outputs the corrected white balance correctionvalue W_(T) (W_(TR), W_(TG), W_(TB)) to the multipliers 52R, 52G, and52B of the white balance correction circuit 52 and performs whitebalance correction.

Further, in the method of recording the white balance correction valuein the EEPROM 76, recording is performed using a communicating functionand a recording medium that are provided in the digital camera, justlike the digital camera 10 of Embodiment 1.

A white balance correction value corresponding to each ambienttemperature T may be uniquely set in all products of digital cameras.However, the LED emits light varied in color temperature among elementsjust like Embodiment 1 and thus it is preferable to perform settingbased on the color temperature of light actually emitted from theelectronic flash device 18.

FIG. 6 is a block diagram showing the internal configuration ofEmbodiment 4 according to the digital camera of the present invention.

As shown in FIG. 6, a digital camera 110 of the present embodiment isdifferent from the digital camera 10 of Embodiment 1 in that anelectronic flash device 18 comprises an ammeter 112 for measuringcurrent (forward current) applied to an LED. Since the otherconfigurations are the same as the digital camera 10 of Embodiment 1,the same components as the digital camera 10 of Embodiment 1 areindicated by the same reference numerals and the explanation thereof isomitted.

The LED serving as a flash light source emits light varied in colortemperature according to a change in current applied to the LED. FIG. 7is an xy chromaticity diagram showing a change in color temperaturerelative to a change in current I applied to the LED (when the ambienttemperature of the LED is 20° C.). As shown in FIG. 7, as the current Iapplied to the LED is reduced, the color temperature of light emitted bythe LED also shifts to a lower temperature.

Therefore, when white balance correction is performed by using aconstant white balance correction value on image data obtained by flashshooting, a change in current applied to the LED may result in images ofdifferent color shades.

Hence, in the digital camera 110 of the present embodiment, a whitebalance correction value is corrected according to a change in currentapplied to the LED.

As shown in FIG. 6, the electronic flash device 18 comprises the ammeter112 for measuring current applied to the LED serving as a light source.A current value measured by the ammeter 112 is inputted to a CPU 60 viaan AD converter 114.

On the other hand, an EEPROM 76 records a table indicating acorrespondence relationship between a current I applied to the LED and awhite balance correction value W_(I) (W_(IR), W_(IG), W_(IB)). By makingreference to the table, the white balance correction value W_(I)(W_(IR), W_(IG), W_(IB)) is uniquely determined according to the currentI applied to the LED.

The CPU 60 acquires the current I applied to the LED, via the ADconverter 114 from the ammeter 112. Then, the CPU 60 determines thewhite balance correction value W_(I) (W_(IR), W_(IG), W_(IB)), whichcorresponds to the current I, based on the table recorded in the EEPROM76. Subsequently, the CPU 60 outputs the determined white balancecorrection value W_(I) (W_(IR), W_(IG), W_(IB)) to multipliers 52R, 52G,and 52B of a white balance correction circuit 52 and performs whitebalance correction on taken image data.

Thus, even when current applied to the LED changes and light emittedfrom the LED changes in color temperature, it is always possible toobtain an image with stable color balance.

In the present embodiment, the white balance correction value W_(I)(W_(IR), W_(IG), W_(IB)) at each current applied to the LED is recordedas a table in the EEPROM 76. A ROM 74 may record a reference whitebalance correction value, for example, a white balance correction valueW₂₀ (W_(20R), W_(20G), W_(20B)) when the current I applied to the LED is20 mA, and the EEPROM 76 may record a modification value ΔW_(I)(modification value of the reference white balance correction value W₂₀at each current I applied to the LED) as a table at each current Iapplied to the LED.

In this case, the CPU 60 acquires the modification value ΔW_(I)corresponding to the current I applied to the LED, from the tablerecorded in the EEPROM 76, and the CPU 60 corrects the reference whitebalance correction value W₂₀. Then, the CPU 60 outputs the correctedwhite balance correction value W_(I) (W_(IR), W_(IG), W_(IB)) to themultipliers 52R, 52G, and 52B of the white balance correction circuit 52and performs white balance correction on taken image data.

Further, in the method of recording a white balance correction value inthe EEPROM 76, recording is performed using a communicating function anda recording medium that are provided in the digital camera, just likethe digital camera 10 of Embodiment 1.

A white balance correction value corresponding to each current I may beuniquely set for all products of digital cameras. However, just likeEmbodiment 1, the LED emits light varied in color temperature amongelements and thus it is preferable to perform setting based on the colortemperature of light actually emitted from the electronic flash device18.

As described above, according to the digital camera of the presentinvention, even when the LED emitting light varied in color temperatureamong elements is used as a flash light source, each product of cameracan obtain an image of the same color shade without being varied incolor balance.

Further, even when emitted light is varied in color temperature due to achange in ambient temperature and a change in current applied to theLED, it is always possible to maintain fixed color balance, achieving astable image.

The series of embodiments discussed that the LED emitting white light isused as a flash light source. The present invention is similarlyapplicable to an electronic flash device which uses, as flash lightsources, three LEDs including an LED emitting red light, an LED emittinggreen light, and an LED emitting blue light.

Moreover, in the above-described embodiments, white-balance processingis performed in the digital signal processing circuit 48. White-balanceprocessing may be performed in an analog signal processing circuitincluding a CDS circuit and a gain control amplifier (not shown).

Further, white balance correction may be performed by multiplying gainvalues to the values of color-difference signals C_(r) and C_(b).

1. A digital camera having an electronic flash device using alight-emitting diode as a flash light source, comprising: a storagedevice which stores correction information for correcting white balanceof an image obtained by flash shooting, a white balance correctingdevice which corrects white balance of the image obtained by flashshooting based on the correction information stored in the storagedevice, a temperature detecting device which detects an ambienttemperature of the light-emitting diode, a modification informationstorage device which stores modification information for modifying thecorrection information stored in the storage device, the modificationinformation storage device storing the modification information of thecorrection information based on a change in an ambient temperature ofthe light-emitting diode, a modifying device which modifies thecorrection information stored in the storage device based on a detectionresult of the temperature detecting device and the modificationinformation stored in the modification information storage device; andthe white balance correcting device corrects white balance of the imageobtained by flash shooting based on the correction information modifiedby the modifying device.